Hydrophobic surfaces bind very weakly with water, which makes drops of water “bead up” on the surface. A hydrophobic surface is generally defined and defined herein as that which has a contact angle greater than 90° with a drop of water. Hydrophobic materials include many well-known, commercially available polymers.
A super-hydrophobic surface is generally defined and defined herein as that which has a contact angle greater than 150° with a drop of water. The lotus leaf surface is known to be naturally super-hydrophobic due to the texture of its waxy surface.
New materials are and methods are being sought that provide capability for making sharp-featured surfaces that are especially suitable for super-hydrophobic applications.
In typical microfabrication and nanofabrication etching processes, care is taken to produce structures with steep sidewalls and/or high aspect ratios. Vacuum etching processes are used because the use of liquid chemical etchants typically results in rounded structures. Even in the process for producing microchannel or nanochannel glass, the materials and etchant are chosen to result in steep sidewalls and extremely high aspect ratios. In the present invention, a novel etching process is used to make structures with intentionally angled sidewalls, resulting in sharpened surface features. The novel process may produce atomically sharp points with a simple, robust process. This is in strong contrast to the usual rounded “wet” etched features or the precise timing and conditions typically needed for vacuum processing.